DYNAMIC STABILITY OF TRAINS MOVING OVER BRIDGES SHAKEN BY EARTHQUAKES

The dynamic stability of trains moving over bridges shaken by earthquakes is studied. Unlike the seismic analysis of structures containing a single subsystem, the seismic analysis of a bridge sustaining a passing train requires not only information on acceleration, but also on velocity and displacement of the ground motion. Four typical earthquakes, including the 1999 Chi-Chi Earthquake, were adopted as the input excitations, each of which was normalized to have a moderate intensity. The results indicate that a train initially resting on the bridge can stay safely under the ground motions considered, if the bridge and track structures do not exhibit inelastic deformations during the earthquake. The type of the vertical component of ground motions can affect significantly the stability of the train–rail– bridge system. As a preliminary attempt, safety, possible instability and instability regions were established in a three-phase plot for the train running over the bridge for each of the earthquakes considered, from which the maximum allowable speed for the train to run safely under the specified ground acceleration can be obtained.